1. Field of the Invention
The present invention relates generally to television receivers and, more particularly, is directed to a television apparatus which displays an output image of a video signal as a strobe action which means that a still image is being sequentially changed.
2. Description of the Prior Art
A television receiver that can display an output image of a video signal as a strobe action has been known previously. In this case, to display an output image as a strobe action is to display the output image of the video signal in such a manner that a still image is being sequentially changed. Such prior art television receiver includes a memory or a video RAM (random access memory) capable of storing a field time (or frame time) of a video signal, in which in the strobe display mode, one field time of an input video signal is stored in the memory within one field period. Then, the writing of that video signal is interrupted, the video signal stored in the memory is repeatedly read over a predetermined period of time, for example, 8 field periods and the video signals of one field period repeatedly read are supplied to and displayed on a cathode ray tube (CRT). Thereafter, the writing of that video signal in the memory is interrupted and one field time of the input video signal is similarly written in the memory within one field period. The above-mentioned operation is repeatedly carried out, whereby the strobe display is performed on the screen of the cathode ray tube in which the image is changed at every 9-field period.
For the strobe display, one proposal is that the strobe display is effected on the whole screen of the cathode ray tube on the basis of a video signal of a certain channel. Another proposal is that the screen of the cathode ray tube is divided to provide two screens, wherein an image on the basis of a video signal of a certain channel is normally displayed on one divided screen, whereas an image on the basis of a video signal of other channel is displayed on the other divided screen in a strobe-display-fashion. Then, the screen for standard display and the screen for strobe display are exchanged with each other at every predetermine period of time.
Writing one field time of an input video signal in the memory within one field period of time, thereafter stopping the writing of the input video signal, reading image data or contents stored in the memory over a desired field period repeatedly and supplying the thus read image data to a cathode ray tube, it becomes possible to display an image on the cathode ray tube as a still image which is one of the strobe display.
In the prior-art television receiver, when the input video signal is selected, or when the channel selection of the received television signal is effected or when the received input video signal and the external input video signals from a video tape recorder, a video disk reproducing apparatus and the like are selected, if the selection period of the input video signal overlaps the writing period of the video signal in the above-mentioned memory, then a video signal disturbed by the shifted synchronization is written in the memory. Thus, when the video signal written in the memory is repeatedly read out and is then fed to the cathode ray tube, then the disturbed image becomes remarkably conspicuous.
To remove the above defects, it is proposed that when the incoming video signal is switched in the period of the strobe display, the strobe display is temporarily stopped or the blanking is applied to the cathode ray tube.
However, it is not preferable that the strobe display be temporarily stopped. Particularly, when the display screen of the cathode ray tube is divided to provide two display screens wherein one video signal of different channels is displayed on one divided display screen in a standard mode, whereas the other video signal is displayed on the other divided display screen in the strobe-action-fashion, or when these video signals are exchanged with each other and are displayed on the two divided display screens, the interruption of the strobe display is not preferable because the interruption of the strobe display presents such a problem that images based on the video signals of different channels are neither displayed on the display screens of the cathode ray tube.
When the incoming video signal is switched in the period of the strobe display, it is not desired that the blanking is applied to the cathode ray tube because the blanking results in the display of image being interrupted.
As earlier noted, according to the prior-art television receiver capable of the strobe display, one field of incoming video signal is written in the memory means over one field period at every 9 (=1+8)-field, or at every odd-numbered field period. Thereafter, the writing of the incoming video signal in the memory means is stopped and one field of the video signal stored in the memory means is repeatedly read out over a time period of 8 fields that are longer than the writing period. Thus, when an incoming video signal is a video signal according to the interlaced scanning system, the odd or even field of the initial video signal written in the memory means at every 9-field period, or at every odd-numbered field is alternately changed in the order of odd, even, odd . . . , so that if the incoming video signal is a video signal of an image having less motion, the image looks as if it were fluctuated in the vertical direction.